1. Field of the Invention
The present invention relates to a method and an apparatus for transferring image data from a terminal to an image server, and to a computer-readable recording medium storing a program to cause a computer to execute the method.
2. Description of the Related Art
When image data stored in an image server are transferred based on transfer request by a client, the client receives and decompresses the data to reproduce an image if the image data have been compressed based on a predetermined coding algorithm.
Meanwhile, as a format for storing image data, various formats such as JPEG, GIF, and TIFF are used. Recently, another format has been proposed. According to this format, image data are stored by being decomposed into a hierarchy based on resolutions or density resolutions (bit resolutions) and data at each level of the hierarchy (hierarchical data) are stored after coding and compression thereof. More specifically, image data are decomposed into the hierarchical data according to multiple resolutions or density resolutions through wavelet transform or the like, and the hierarchical data at each resolution or density resolution are coded according to the hierarchy and saved in a file after compression thereof.
This storing method has the following characteristics:    (1) Unlike a DCT (Discrete Cosine Transform) method used in the conventional JPEG format, no artifacts such as block distortion are created, since image data are not processed for each block.    (2) Only resolution information which is necessary for transfer of image data needs to be transferred, since the image data are coded hierarchically. This enables efficient image transfer.    (3) Various kinds of image processing such as frequency enhancing processing can be carried out comparatively easily, since image data are decomposed into the data at multiple resolutions or density resolutions.    (4) Simultaneous decomposition of space and frequency according to multiple-resolution analysis is possible. In a low frequency range wherein coding efficiency is greatly affected, an orthogonal transform can be carried out in a wide range, whereas in a high frequency range, an orthogonal transform is possible in a narrow range. Therefore, even when quantization noise is generated near an edge of an image, spatial spread of the noise can be suppressed. As a result, the noise is not easy to perceive.
Like a FlashPix file proposed by Eastman Kodak Co., a file format enabling storage of data sets having different natures in a file has also been proposed. Hierarchical data decomposed into multiple resolutions or density resolutions can be stored in such a file according to the FlashPix standard.
By decomposing the image data into multiple resolutions or density resolutions, the image data can be reconstructed from data at a plurality of levels having different resolutions or density resolutions.
Furthermore, it is possible to construct image data representing an image from data at a plurality of levels representing the same image each having different quality when the image is reproduced. In other words, image data obtained by decompressing image data having been compressed in a reversible manner have no degradation, while image data obtained by decompressing image data having been compressed in an irreversible manner have degradation depending on a sampling interval of the data. Therefore, quality of a reproduced image can be changed according to whether image data are compressed in a reversible manner or in an irreversible manner. Consequently, image data can be reconstructed from the data at a plurality of levels having different reproduced image quality.
When image data are constructed from data at a plurality of levels and stored in an image server in this manner, data at an appropriate resolution or density resolution or having appropriate quality of a reproduced image can be transferred to a client based on the client's request, and the client's request can be met.
Furthermore, a method of transferring image data to a terminal connected to an image server having means for storing an image data set in detail, that is, data at a high level (high resolution or density resolution, or high reproduced image quality) and for converting a level of the image to be output, instead of an image server storing image data at a plurality of levels, has been known. In this case, as has been described above, data at an appropriate level can be transferred to the client based on the request by the client.
However, the level of the data requested by a client is different depending on a user of the terminal, the type of the terminal, and the usage of the image data. For example, the level of an image requested is different between the cases of a diagnostic purpose such as a diagnosis in detail, a confirmation purpose such as confirmation of an outline, and taking a view of an outline image such as subtraction at an interval. Furthermore, the level requested is different between wards or doctors, and each has a predetermined level in most cases.
For this reason, it is necessary to specify the level of data desired by a client by inputting the level whenever image data transfer is requested. As a result, an operation for requesting data transfer is very troublesome.